The invention relates to a small sized electric motor and more particularly relates to a small sized electric motor which is sectionally non-circular and may be used in various machines and apparatuses and which has the fulcrums of brushes arranged in the direction lengthwise of the section of motor, so that brushes of sufficient length may be used in the small sized electric motor.
The conventional small sized electric motor 1 is generally non-circular in the section thereof as shown in FIG. 3 because a motor of such outer configuration may be more easily attached to the machines and other apparatus. In FIG. 3, the conventional small sized electric motor 1 (called a motor hereinafter) has a sectionally rectangular housing 2, in which a pair of magnets 3, 4 are oppositely arranged in the direction lengthwise thereof and a rotor 5 is rotatably positioned between the two magnets. FIG. 3 shows a triplepolar motor 1 as an example of multipolar motors, in which the rotor 5 is composed of a rotor shaft 7, rotatably journalled in the housing 2, a rotor core structure 8 which is assembled integral with the core shaft 7 and formed with cores 8a, 8b, 8c providing winding carrier parts 8d, 8e, 8f respectively, a winding 9 sequentially wound around the winding carrier parts 8d, 8e, 8f, connector terminals 10 provided between the winding carrier parts respectively and extending radially of the rotor shaft 7. The terminals each having connected thereto the initial and last ends of the winding 9 wound around the winding carrier parts 8d, 8e, 8f, and a commutator 11 mounted on the rotor shaft 7 and providing conductive parts 11a, 11b, 11c and nonconductive parts 11d, 11e, 11f.
The core structure 8 has the winding carrier parts 8d, 8e, 8f arranged around the rotor shaft 7 with a space of 120.degree. therebetween, and accordingly the connector terminals 10a, 10b, 10c are arranged on the commutator 11 with a space of 120.degree. therebetween. Similarly the commutator 11 has the nonconductive parts 11d, 11e, 11f each arranged between the adjacent winding carrier parts 8d, 8e, 8f with a space of 120.degree. therebetween around the rotor shaft 7.
The winding 9 has the initial end anchored, for example, to one 10a of the connector terminals 10 of the commutator 11, and then is wound a predetermined number of times around the winding carrier part 8b of the cores. The wound end 9b is anchored to the next connector terminal 10b where the initial end 9c of the winding 9 starts again to be wound around the next winding carrier part 8f of the cores. After the winding 9 has been wound the predetermined times around the winding carrier part 8f, the wound end 9d is then anchored to the next connector terminal 10c where the initial end 9e of the winding 9 starts again to be wound around the next winding carrier part 10c. After the winding 9 has been wound the predetermined number of times around the winding carrier part 10c, the wound end 9f is then anchored to the initial connector terminal 10a. Then the initial and wound ends of the winding 9 are each welded to the respective connector terminals
A pair of linear brushes 12, 13, which are passed against the commutator 11 on the opposite sides thereof with the an elasticity of their own, have the respective base ends 12a, 13a secured to the associated fulcrums 14, 15 which are provided with a predetermined space therebetween on one side of the housing 2 in a direction laterally thereof. Therefore the brush terminals (not shown), which are to be connected to a power supply (not shown), are designed to outwardly project side by side from the side of the housing 2 in the direction laterally thereof.
The brushes 12, 13 are adapted to cooperate with the nonconductive parts 11d, 11e, 11f of the commutator 11 as the rotor 5 is rotated to thereby change over the direction of electric current flowing through the winding 9 wound around the winding carrier parts 8d, 8e, 8f of the cores 8a, 8b, 8c, i.e. to determine the electric displacement position of the commutator 11, so that the rotor 5 may be continuously rotated. In this case, the nonconductive parts 11d, 11e, 11f are positioned in alignment with the center axes of the respective winding carrier parts 8d, 8e, 8f of the core structure 8, and accordingly the electric displacement position of the commutator 11 is 0.degree. with respect to the magnetic line of force M of the magnets 3, 4. Namely if the rotor 5 is rotated in the direction as shown by an arrow A, the direction of electric current flowing through the winding 9 on the winding carrier part 8e is changed over when the nonconductive part 11f of the commutator 11 contacts the brush 12. When the nonconductive part 11 e contacts the brush 13, the direction of electric current flowing through the winding 9 of the winding carrier part 8d is changed over, and when the nonconductive part 11 d contacts the brush 12, the direction of electric current flowing through the winding 9 of the winding carrier part 8c is changed over. Thus the rotor 5 is continuously rotated.
Now according to the conventional motor 1, since the brushes 12, 13 are arranged extending in parallel with each other from one side of the casing 2 in the direction laterally thereof in such a manner as to transverse the magnetic line of force M of the magnets 3, 4, the length of the brushes 12, 13 is extraordinarily delimited with respect to the commutator 11. Namely in the prior art, since the distance is very short between the fulcrum of each brush and a point of the commutator where the brush contacts the commutator, the pressing variation of the brush is accordingly large to the extent that the contact of the brush with the commutator is not stabilized, and therefore the output of the motor is lowered. Further as the brushes and commutator come to be worn down, the contact angle of brushes with respect to the commutator will be remarkably varied, and accordingly the electric displacement position is varied. As the result, the output of the motor is further lowered. Still further, in the assembling operation, it is almost impossible to avoid the variations of angle with which the brushes are attached to the fulcrums. Such variations of attaching angle will inevitably result in variations of pressure with which the brushes contact the commutator. The foregoing disadvantages have been typical in the small sized electric motor.